Intermittent and persistent shedding ofEscherichia coliO157 in cohorts of naturally infected calves.

s.e. robinson, e.j. wright, c.a. hart, m. bennett and n.p. french. 2004.We conducted two short-term studies of cohorts of naturally infected calves to determine the prevalence and concentrations ofEscherichia coliO157 shed in faeces.Two cohorts of calves were sampled; in the first study 14 calves were sampled up to five times a day for 5 days; in the second study a group of 16 separate calves were sampled once or twice a day for 15 days. All cattle within the two cohorts shedE. coliO157 at some point during the respective studies. In 18% of samples,E. coliO157 could only be isolated using immunomagnetic separation after an enrichment period, suggesting concentrations<250 CFU g−1. The highest concentrations recorded were 6·7 × 105 and 1·6 × 106 CFU g−1 for studies 1 and 2 respectively.Persistent, high shedders (shedding>103 CFU g−1) were evident in both studies but, in the majority of calves, the pathogen was isolated intermittently.The variable patterns of shedding have important implications for the design of appropriate sampling protocols and for gaining meaningful estimates of parameters used in mathematical models of transmission. [ABSTRACT FROM AUTHOR]